Tuned circuit and system therefor



y 2, 1 6- w. VAN B. ROBERTS TUNED CIRCUIT AND SYSTEM THEREFOR F 'iled Sept. 26, 1942 Tuz i.

2 Sheets-Sheet 1 INVENTOR #4052 mm b.

$055270 /unm,

ATTO R N EY y 1946- W. VAN B. ROBERTS 2,403,151 TUNED CIRCUIT AND. SYSTEM THEREFOR 2 Sheets-Sheet I INVENTOR Mum? mm 5.. IPOEERTJ.

Filed Sept. 26. 1942 ATTORNEY Patented July 2, 1946 TUNED CIRCUIT AND SYSTEM THEREFOR Walter van 13. Roberts, Princeton, N. J., assignor to Radio Corporation of Delaware 1 America, a corporation Application September 26, 1942, Serial No. 459,784

The present invention relates to tuned circuits and associated electron discharge device systems,

16 Claims. (Cl. 178-44) and more particularlyto an electron discharge device amplifier system employing a novel type of endless tuned circuit in the form of a transmission line which is-closed upon itself.

It is known to employ quarter wavelength or half wavelength sections of transmission line in vacuum tube amplifier systems for use as tuned circuits. Examples of these are concentric line tanks, However, an ordinary quarter or half wave linear tank circuit is not suitable for amplifying waves of arbitraryshape, because the end effects of the line make its length unequal to an integral multiple of a quarter or half wave at the harmonic frequencies of the arbitrary wave. The present invention avoids such end effects by employing a linear tank circuit in the form of a transmission line which is closed upon itself so as to be endless, and in which the velocity of wave propagation is independent of frequency.

The design of ordinary lines to meet this latter requirement is well known in the art, the condition of uniform transmission velocity being that the ratio of effective inductance per unit length of line to eifective capacity per unit length be equal to the ratio of effective series resistance per unit length to effective shunt conductance per unit length. v

A'more detailed description of the invention follows in coniunction with drawings wherein:

Fig. 1 shows a known type of amplifier system; Fig. 2 shows a structure'equivalent to that of m and Figs. 3 to 6 show diflerent embodiments of the present invention.

In the drawings, Fig. 1 shows a pair of half wavelength linear tank elements I and 2 in the form of concentric lines connected in parallelin the output circuitof a vacuum tube amplifier 3. The waves to be amplified are impressed on the input electrodes of the tube 3 by source '4. Obviously, the potentials at the open ends O.of the lines I, 2 will be equal and, therefore, the open remote ends may be connected together without alteration of the performance except that end eflects are avoided. If this is done, the resulting structure may be of circular form (as shown in Fig. 2 and identified by reference character where the perimeter is afull wave of the operating frequency. The tank i shown in Fig. 2 .would be useful .for amplifying waves of arbitrary form if the capacity of the vacuum tube 3 were neg- 2 being a current node at the tube and at the point diametrically opposite. These standing waves may be considered as the sum of the two traveling waves going in opposite directions around the tank 5.

Fig. 3 shows oneembodiment of the present invention in which a similar tank 5' is shown energized by a plurality of vacuum tubes 20, 2|, Hand 23 which are excited in phase displacement. For example, the top tube is excited by sinusoidal wave source 3' at a frequency equal to the frequency of rotation of an electromagnetic disturbance around the tank I. This vacuum tube 20 can be considered to excite a pair of traveling waves in opposite directions. The right hand tube 2| is excited with the same frequency from source I but with a 90 phase displacement. This vacuum tube 2| also sets up a pair of oppositely traveling waves. Assuming that the excitation of the right hand tube 2| is '90? ahead of that of the upper vacuum tube 20. it will be seen that counter-clockwise traveling waves from the two tubes 20 and 2| will be of similar phase and, hence, willbe additive; while clockwise traveling waves will be of opposite phase and hence cancel each other. Thus, the net result will be a single wave traveling counterclockwise. Another pair of vacuum tubes 22 and 23 similarly related are also shown at the bottom and at the left side of the tank I, the bottom vacuum tube 22 being excited in phase. opposition to the top tube 20 and the left tube 23 being excited in phase opposition to the right hand one 2|. -It will be seen that any number of tubes may be distributed around the tank provided their phases of excitation are progressively shifted so that they all impart energy to the traveling wave as it passes. If a large number of vacuum tubes is' Q employed, the constants of the line are eflectively ligible. In Fig. 2 the waves in the circular tank .I a'reofthe type known as standing waves. there uniformly distributed. then be made of small .power capacity small electro-static capacity. a

a primary object of the endless tank circuit is to provide a means for amplifying waves of other shapes than sinusoidal. As an example, Fig. 4

Each vacuum tube may shows a system for generating low voltage sawtooth waves which are then amplified in one'or more circular tanks, endless tank II having associated therewith a plurality of amplifier vacuum tubes 25. Operating class .A, only two of which are here shown. The

letter S'indicates a view along the axis of a o'athode ray tube whose electron beam 3 is caused'to trace a circle and thereby to pass successively across the various separated mm a anodes and hence Inr'lg.4thereisshownanplate connection points I P, P. A substantially constant current is araway. If a traveling wave is counterclockwise, then as its positive peak passes the anode of the tube 35 its grid will also receive a positive peak of voltage, and hence the tube 35 will act as a shunt conductance and absorb energy from the wave. On the other hand, if the wave is assumed to be traveling clockwise, then the grid .will be driven positive at the instant when the plate potential is a minimum and hence the tube and amplifier tube is connected to each of the anodes P and the various-amplifier vacuum tubes are connected to points uniformly spaced around the endless tank. The electrical length of this tank is so chosen that electromagnetic disturbances (sawtooth traveling wave) around it with the same frequency that the electron beam B revolves. Thus, each of the amacts to reinforce the sawtooth wave as it travels around the tank and passes the tube in question. If these vacuum tubes are of w a type capable of producing a high voltage gain between input voltage and plate voltage, then the sawtooth wave circulating in the tank will be of greatly increased amplitude as compared to the wave generated across condenser C. However, if the amplitude is still insufiicient, a second stage of amplification may be provided which uses a similar circular tank I 5 fed from a plurality of spaced amplifier tubes 25' eachof which is excited from travel correspondingly spaced points in the first mentinned tank l5, as shown. Preferably, such excitation points should be chosen intermediate the on the first tank l5 so that the lumped capacities across the will be as uniformly, distributed as possible. It will be evident that this method of amplification may be applied to any desired wave form and that almost any desired wave form may be obtained at will act as a negative conductance across the line and increase the energy of the wave. Actually, a plurality of vacuum tubes 35, 36, 31 and 38 should be connected to the line at spaced points but in similar fashion,v as shown. An advantage obassumed to be goin I tained by generating oscillations with many tubes connected at various points around such a line -45 in the manner illustrated is that large amounts of power may be fed into the tank 45 without introducing large lumped capacities at any point.

In the-foregoing, it has been assumed that the wave period is equal to the time of travel around the tank. However, it will be seen that the time of travel may be any multiple of the wave period with the result that not one but several waves will be traveling around the tank. The phase relations will in this case be determined by the electrical degrees around the tank' for the wave employed rather than the angle measured around the tank itself.

A circular tank may be used for combining waves of harmonicallyrelated frequency since,-

as explained before, it is devoid of end effects. For example, in Fig. 3 the upper and right hand vacuum-tubes 20 and 2t may be employed todevelop a fundamental frequency traveling wave, while the other two tubes 22 and 23 may be excited at a harmonic frequency and-so located as to set up a. harmonic wave traveling in the 4 same direction. Similarly. additional pairs of low voltage levelsby the use of suitably shaped electrodes in a cathode ray device.

Fig. 5 shows the endless tank It applied to the problem of amplifying an arbitrary wave form which cannot readily be generated as a multiple series of waves with time displacement between them. In Fig. 5 the source of waves is shown at E, and these waves travel along a line TL terminated at T in its characteristic resistance so as to avoid reflection. Thus, the various amplifier tubes ll, l2, 13, etc., receive excitations which are automatically successively delayed by the right amount if the exciting line TL is located alongside the output tank III or, at any rate, if the two lines TL and II are so related as to length and velocity of propagation that waves travel in each of them with the same angular velocity. In this case again, any number of tubes may be employed, but in order to obtain the eifect of uniformly distributed constants in the line tank l0 without em playing an excessive number of vacuum tubes. small lumped capacities 5, 6 correspondin to tube may be placed across the line, instead of tubes. All of the vacuum tubes are preferably connected in the same way to the tank ll, although such connection may be capacitive or inductive instead of the direct connection as shown. A unidirectional traveling wave in an endless tank may be sustained by feed back action, as shown in the oscillator system of Fig. 6, where there is shown an endless tank 45 and a time detubes may be added to develop other harmonics and by a suitable adjustment of the phases and amplitudes of excitation the various waves may be caused to add up to produce a resultant wave form approximating any desired shape in accordance with the well-known Fourrier analysis of periodic wave shapes.

It. should be understood that while a circular tank has been shown, such, a. shape is not im-- portant, and in case the dimensions of the circular tank would be inconveniently large the tank may be folded up in any desired fashion, for example so as to bring the points of connection of the tubes to desired locations.

I It is further contemplated that for operation with vacuum tube constants as uniformly distributed as possible, the endless line structure itself may be composed of continuous vacuum tube electrodes as disclosed in my Patent No. 2,168,782, issued August ,8, 1939. In accordance with this patent, a continuously distributed negative conductance may be provided along a, transmission line or a negative conductance may be provided in sections of the line without interrupting the smooth character of the line impedance.

Output from any of the endless tuned circuits may be taken by means of a link circuit, such as within the tuned circuit, or by means .of a direct I a wire loop, entering the tank or tuned circuit at any desired point and enclosing magnetic flux or capacitive connection to the inner conductor lay circuit 1- used for feeding voltage from a'point on the circuit to a vacuum tube 35 ,whose'output circuit is connected to the tank 45 at a point of the endless tuned circuit at any desired point. If more than one output circuit is connected to the tank, any desired phase displacement between 1c the several outputs may be obtained by connecting the outputs at points suitably displaced from each other around the tank.

What is claimed is;

1. The combination with a tuned circuit com prising a two-conductor transmission line closed upon itself to form an endless structure of uniformly distributed constants. the conductors of said tuned circuit being electrically continuous from a direct current standpoint, of a plurality of vacuum tubes having their output electrodes coupled at spaced points to said tuned circuit and their input electrodes so excited that the output of said tubes increases the energy of the traveling waves in said tuned circuit, rather than the energy of the standing waves.

2. The combination with a tuned circuit adapted to be energized by a traveling wave continuously moving in one direction in said tuned-circuit and comprising an endless structure in the form of a transmission line closed upon itself, of a plurality of vacuum, tubes coupled to said line at spaced points along said line, and means for exciting said tubes with energy of the same fre-' quency but with a predetermined phase displacement to thereby increase the energy of said traveling wave without causing an opposite traveling wave. v

3. An amplifier system comprising a plurality of electron discharge devices each having an input electrode and an output electrode, a tuned circuit in the form of an endless transmission line whic is closed upon itself, connections coupling the output electrodes of said devices in similar manner to diflerent spaced portions 01' said tuned circuit, and means for exciting the input electrodes of said devices with energy of the same frequency but of progressively shifting phase.

' whereby all output electrodes of said devices add energy substantially only to the wave traveling along the length of said tuned circuit in one direction.

4. An amplifier system comprising a plurality of electron discharge devices each having an input electrode and an output electrode, a tuned circuit in the form of an endless transmission line which is closed upon itself, connections 0011-1 pling the output electrodes of said devices in similar manner to diflerent spaced portions of said tuned circuit which are uniformly spaced around the tuned circuit, and means for exciting the input electrodes of said devices withenergy oi the same frequency but of progressively shifting phase, whereby all output electrodes of said de vices impart energy substantially solely to the wave traveling along the length of said tuned circuit in only one direction.

5. An amplifier system comprising a plurality of electron discharge devices each having an. input electrode and an output electrode, a tuned circuit in the form of an endless transmission line which is closed upon itself, connections coupling the output electrodes of said devices in similar manner to ditl'erent spaced portions 01' said tuned circuit, and means'for exciting the input electrodes of said devices with energy of the same frequency but of progressively shifting phase. whereby all output electrodes of said devices impart energy substantially solely to that wave. traveling along the length of said-tuned circuit in one direction only, the frequency oi! the wave tobe amplified being equal to the time of travel around said endless tuned circuit.

6. An amplifier system, comprising a tuned circuit in the form of an endless concentric transmission linewhich is clomd upon itself,-'a sec- 6 tion oi ton line arranged adjacent to and parallel with said first tuned circuit, means for producing a wave traveling'in onedirection along the length oi said section of transmission line, a plurality of spaced electron discharge devices each having a cathode, an anode and a.

grid, connections from the grids of said devices to diflerent points along the length of said section of transmission lineso chosen that the.

phases of excitation of said devices are progressively shifted, and connections coupling the anodes of said devices to diii'erent portions 01' the inner conductor of said endless tank so chosenat a plurality 01' points along its length.

9. An electron discharge devicesystem comprising a tuned circuit in the form of an endless concentric transmission line which is closed upon itself, a section 01- transmission line arranged adjacent to and parallel with said first tuned circuit, means for producing a wave traveling in one direction'only along the length oi said section of transmission line, a plurality of spaced electron discharge devices each having a cathode, an'anode anda grid, connections from the grids of said devices to diflerent points along the length of said section of transmission line so chosen that the .phases of excitation of said de.-'

vices are progressively shifted, and connections coupling the anodes or said devices to diii'erent portions of the inner conductor of said endless concentric line so chosen that said devices impart energy to the wave traveling around said endless, concentric line, the dimensions of both of said transmission lines being so related as to length and velocity oi propagation that waves travel in each 01 them with the same angular velocity.

10. The combination with. a tuned circuit adapted to be energized by a traveling wave continuously moving in one direction only in said tank and comprising an endless structure in the form of atransmission line closed upon itself,

of a plurality of vacuum tubes coupled to said line at spaced points along said line, means for exciting said tubes with energy of the same frequency but with a predetermined phase displacement to thereby add to the energy 01'. said travelingwave, and at least one additional plu- 1 rallty of similarly connectedtubes connected to said transmission line and excited at a harmonic frequency to produce a harmonic wave traveling in the same direction, whereby the resultant traveling wave shape is the wave shape whose Fourrier components ages. 1

ii. The combination with a tuned circuit comprising a two-conductor transmission line closed upon-itself to-form an endless structure oi uniare the said excitation voltformly distributed constants. the conductors of said tuned circuit being electrically continuous from a directcurrent standpoint. of a plurality of vacuum tubes having then-output electrodes coupled at spaced points to said tuned circuit, and

- asoaisi means for exciting the input electrodes of said tubes with energy .of the same frequency but with a predetermined phase displacement, to thereby cause the output of said tubes to increase the energy of waves traveling in One direction only in said endless line, the period of the exciting wave being equal to the time of travel of energy around said line.

12. An electron discharge device system including an endless tank of uniformly distributed constants and means for setting up in said tank a traveling wave traveling in one direction only,

such that there is uniform current in all parts of said tank, said means including'a pluralit of vacuum tubes having output electrodes coupled to different spaced points on said tank, and circuits for exciting the input electrodes of said tubes with energy of progressively shifting phase,

whereby all of said tubes add energy to said travwhereby all of said tubes add energy to a wave traveling around said line, said circuit including a multi-target cathode ray device whose electron beam traverses a circle and successively impinges I on said targets, there being connections from different targets of said cathode ray device to different input electrodes of said vacuum tubes.

14. An amplifier system comprising a tuned circuit in the form of an endless concentric transmission line which is closed upon itself, a section of transmission line arranged adjacent to and parallel with said first tuned circuit, means for producing a wave traveling in one direction along the length of said section of transmission lin including a source of alternating current at one end of the section and an impedance at the other end of said section for terminating said section in its characteristic resistance so as to avoid wave reflection, a plurality of vacuum tubes having their output electrodes coupled at spaced points to the inner conductor of said endless concentric line, and their input electrodes coupled at spaced points to said section of line, said endless line and said section of line being sc related as to length and velocity of propagation that waves travel in each of them with the same angular velocity,

15. The combination with a tuned circuit' adapted to be energized by a traveling wave continuously moving in one direction. in said tuned circuit and comprising an endless structure in the form of a transmission line closed upon itself, of a plurality of electron discharge device generators of periodically repeating waves, connections irom the output electrodes of said generators to spaced points on said tuned circuit, and means for supplying the input electrodes of said generators with currents of relatively progressively shifting phase. i

16. The combination with a tuned circuit adapted to be energized by a traveling wave continuously moving in one direction in said tuned circuit and comprising an endless structure in the form of a transmission line closed upon itself, of a plurality of electron discharge device generators of saw-tooth waves, connections from the output electrodes of said generators to spaced points on said tuned circuit, condensers in circuit with the input electrodes of said generators adapted to be charged and discharged, and means for supplying said input electrodes with electron beam currents of relatively progressively shitting hase. I t

WALTER VAN B. ROBERTS. 

